Is focussed stimulation by parents effective to improve vocabulary in Down syndrome?

The next article that we will discuss in our series of blog posts related to our systematic literature review is entitled ‘Vocabulary intervention for young children with Down syndrome: parent training using focussed stimulation’, by Girolametto, Weitzman and Clements-Baartman (1998).


The study assessed the effect of training parents of children with Down syndrome to use a technique called focussed stimulation, to improve their children’s vocabulary. The idea is that language development is stimulated by the parent ‘modelling language at their child’s level during naturally occurring situations’ (pg. 110), and parents receive training to do this in various ways to target specific language goals. The details of techniques involved in the focussed stimulation approach are outline further on in this post under the intervention details.


There were 12 children included in the study (mean age: 29-46 months), randomly allocated to either the training group or to the control group. The children in the study communicated using single words or signs at the outset.

Children in the experimental group did not receive other therapy programs during the training period. The children in the control group carried on receiving language intervention services during the course of the experimental phase as it was part of their pre-school program. As the authors note, it would be preferable to have a no-treatment control group for comparison.


In a first pre-test session children were videotaped during 15 mins of free play with their mother during which the speech sounds checklist (Girolametto, Pearce, & Weitzman, 1994) was completed by a speech-language pathologist. They also completed various scales to assess vocabulary.

Prior to a second pre-test session 20 target words were selected for each child. The target words were chosen on the basis of being words that the child could comprehend but not produce. The words were those that are acquired by most typically developing children at 24 months of age, and each word started with a phoneme that the child had in their speech sound repertoire (able to make that sound). Finally the words had to be relevant in terms of being functional early in development.

In the second pre-test session, interviews with mothers were carried out to check that children did not already use any of these target words at home, and if they did use a target word already then it was replaced with a different one.


Mother-child free play sessions were again videotaped, assessments taken at pre-test were repeated and children were given naturalistic semi-structured probes, i.e., an object that represented the child’s target words, to assess the child’s expressive use of the 20 target words.

Intervention details:

The Hanen Program (Manolson, 1992; see for more details) was used, this has thorough parent handbooks and videotapes to follow, along with the language stimulation program. The mothers were given the 20 target words and picked 10 that they thought would be most motivating for their child to learn. Parents kept diaries of the children’s word use, and if a child made use of one of the target words spontaneously on 3 occasions, and in 3 different contexts then it was replaced by another word from those remaining on the list.

The program was 13 weeks long; spread across the 13 weeks there were 9 evening sessions to teach parents the techniques (each 2.5 hours long) and four home visits to give parents feedback on their techniques. The authors provide a week by week description of the program content, so that it is clear what was done at each stage. We will not outline each week here as of course the full details can be read in the article but to summarize some key components; parents record and watch back videotapes of interactions with the child, they also watch lectures given by clinicians, including roleplays of how to carry out techniques, and they review techniques based on watching back videotapes, with feedback. The parents are taught to follow the child’s lead. Below are some of the key techniques used across the weeks:

·         Observing waiting and listening

·         Imitation

·         Asking for clarification

·         Commenting

·         Encouraging the child to participate

·         Learning how to ask appropriate questions to encourage turn taking.

·         Using signs to accompany verbal labels

·         Expanding verbal utterance by techniques such as emphasising the word.

·         Adapting songs to facilitate target word learning.

·         Suggestions to increase child’s exposure to books and print.

·         Making book reading interactive.

·         Child centred play – exploratory, creative and flexible.

·         Making use of target words during interaction, but based on the child’s interest, e.g., use the word in the game the child wants to play.

·         Clinician to coach techniques as and when necessary during home visits.



Treatment fidelity was assessed via parental attendance data at the parent training sessions, consumer evaluations, and reports from the home visit by the speech-language pathologist. There was a high level of commitment to the program and parents who missed any session were updated on the next session.


The authors checked that the groups did not differ significantly at pre-test for age, vocabulary size, speech sound inventory, play level, receptive language age, and all outcome measures.

Regarding the mothers there was a significant difference between those in the experimental vs control groups for the rate of talk per minute at post-test. The two groups of mothers did not differ at post-test with regards to the complexity of their language or their mean length of utterance. In the experimental group the mothers used the target words significantly more than the control mothers and used more focussed stimulation of these words.

With regards to the children, the two groups differed significantly at post-test in terms of parental report of the amount of target words produced, with the experimental group using twice as many. The children in the experimental group also used the target words significantly more in free play interactions than did the children in the control group. The frequency of target use was very low in the videotaped interaction for the experimental group (median = 1.5), however this was still greater than the control group since for the control group it was practically non-existent. The two groups did not however differ significantly in their use of target words during the semi-structured probes task.

For the overall vocabulary size estimate there was no significant difference between the two groups of children. From the data reported in the article (medians and ranges) it looks as though the control group actually have much greater gains in overall vocabulary size. It is problematic in terms of showing how very little the effects generalize to vocabulary, and that the control group are doing numerically better here. Of course, the small sample size also comes into play here with the difficulty to interpret, as there are only 6 in each group. The authors note the need for a replication to really make any claims based on these findings for the future, this of course limits the conclusions from the study.

Other limitations:

Although group differences were not significant at pre-test it is worth considering in these types of analyses the influence that even non-significant pre-test differences can have on interpretation of subsequent post-test differences (hence one would usually use a repeated measures design to compare before vs after in each group). Take for example two groups whereby one group starts with a score of 10 and the other a score of 18, if both groups achieved 22 at post-test there would be no difference between their post-test scores, however for the group who began at 10 this is an improvement of 12 compared to just 4 for the other group. Thus, although pre-test differences may not have reached significance, it can be important to consider the relative degree of improvement in the two groups.  This does not apply for the target words in the current study, as, for all children these words were unknown at pre-test, but for variables such as vocabulary size it is a consideration.

As already noted, the study has a very small sample size, which leads to a lack of power. A problem that we have seen in many of the language interventions for those with Down syndrome.

Again, generalisability however was clearly lacking. The authors note that this could be due to the study being too brief, a lack of statistical power, or that perhaps children with Down syndrome do not easily generalise word learning activities to new words. It is of course nothing new to say that we need to look at ways to encourage and promote generalisation, an issue for all interventions regardless of population. Nonetheless, having the tools to directly improve target vocabulary, chosen on the basis of carefully considered criteria, such as functional relevance, is important in itself.

Liz and Kari-Anne


Girolametto, L., Weitzman, E., & Clements-Baartman, J. (1998). Vocabulary intervention for children with Down syndrome: Parent training using focused stimulation. Infant-Toddler Intervention: the Transdisciplinary Journal, 8(2), 109-25.

Girolametto, L., Pearce, P. S., & Weitzman, E. (1994). Speech Sound Checklist. Unpublished manuscript.

Manolson, A. (1992). It takes two to talk: A parent’s guide to helping children communicate. Toronto, ON: The Hanen Centre.

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