ACQ Vol 13 No1 2011

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ACQ Volume 13, Number 1 2011 23
Figure 2 shows the percent correct for word-initial clusters
that were not directly targeted by participants in either
intervention group. The two children who received PAS
intervention made some improvement on the non-target
word-initial clusters, but this was evident only when tested
3 months post-intervention. Neither child who received the
MS intervention program improved in their production of the
non-target word-initial clusters between the pre-intervention
testing and the 3-month post-intervention follow-up.
However, it should be noted that Ben, who received MS
intervention, could accurately produce word-initial labial+/l/
clusters and /s/+nasal clusters pre-intervention. His pre-
intervention accuracy on /s/+nasal clusters may account
for his improvement in the production of /sp/, /st/ and /sl/
clusters even though he did not receive intervention that
directly targeted these clusters.
additional production probes was 0%, except for Aaron who
produced final consonants with 12.5% accuracy.
Reliability
Treatment fidelity was measured by asking an independent
observer to observe videotapes of a random selection of
25% of the total intervention sessions implemented. These
sessions were reviewed to ensure inclusion of important
treatment elements. Treatment fidelity for all PAS and MS
intervention sessions was 100%. Reliability of phonetic
transcription was measured by asking a second person
experienced in transcribing children’s speech to
independently transcribe a random selection of 25% of the
total consonant cluster probes administered. Inter-judge
agreement for broad phonetic transcription of the consonant
clusters was 94%.
Results
Accuracy on consonant cluster probe
In order to investigate the effect of the two different types of
intervention on the production of consonant clusters,
accuracy on the cluster probe was calculated for each of the
four participants at three different points in time (pre-
intervention, immediately post-intervention, and 3 months
post-intervention). Figure 1 shows the percent correct for the
word-initial clusters that were directly targeted in the first
intervention block by participants who received PAS
intervention. None of the participants in either intervention
group could produce this cluster type, pre-intervention.
Immediately post-intervention, one participant from each
intervention group had reached 30% accuracy on this cluster
type, so there was no difference between the groups on this
measure. Thus, Ben, who received MS intervention,
improved in his production of word-initial /sp/, /st/, and /sl/
clusters over the course of the intervention, even though the
intervention he received did not target this particular error
pattern. Both these children show continued improvement in
their production of /sp/, /st/, and /sl/ clusters when tested 3
months after the end of the intervention. It should be noted
that Aaron, who received PAS intervention, did not improve
in his production of word-initial consonant clusters when
tested immediately post-intervention even though he had
received intervention that directly targeted this cluster type.
100
90
80
70
60
50
40
30
20
10
0
Target word-initial clusters
Percent correct
Aaron Mike Matt Ben
PAS intervention MS intervention
3 months post
post-intervention
pre-intervention
Figure 1. Percent correct for word-initial clusters that were
directly targeted by participants who received PAS intervention.
Scores are shown for the two children who received PAS
intervention and for the two children who received MS
intervention.
100
90
80
70
60
50
40
30
20
10
0
Non-target word-initial clusters
Percent correct
Aaron Mike Matt Ben
PAS intervention MS intervention
3 months post
post-intervention
pre-intervention
Figure 2. Percent correct for word-initial clusters that were not
directly targeted by either intervention
Figure 3 reports the percent correct for word-final clusters
that were not directly targeted by participants in either
intervention group. Because participants in the MS group
had received indirect instruction on a variety of consonant
clusters at the ends of words as part of the instruction they
received in word-final morphology, it was predicted that they
would make greater improvement than children in the PAS
group in their production accuracy of word-final clusters.
Surprisingly, only the participants that received the PAS
intervention (Aaron and Mike) improved in their accuracy of
word-final clusters. Both children in this intervention group
showed improved accuracy on final clusters when tested
immediately post-intervention. However, this improvement
was not maintained when Aaron was tested at the 3-month
follow-up. Mike, on the other hand, continued to improve in
his production of word-final clusters. When tested 3 months
post-intervention, he accurately produced 6 out of 8 final
clusters with the remaining two clusters being produced as
2-element clusters where previously they had been reduced
to a single consonant. The only errors in Mike’s production
of word-final clusters were in place of articulation (desk
produced as /dEst/ and wings produced as /wImz/).
Accuracy on singleton target phonological
error pattern
All participants received six sessions of intervention on a
target phonological error pattern that did not involve
consonant clusters (final consonant deletion for Aaron and