How to measure progress for kids with phonological disorders

When treating children with phonological disorders, there are lots of ways we can gauge their progress. Do you measure the child’s speech sound inventory, calculate percent consonants correct (PCC), use overall intelligibility measures, or use probes you created? A combination of these? Nothing at all? (Eek!)


Smit et al. conducted a randomized controlled trial to determine which outcome measures were more sensitive to changes in children’s speech over time. If you’re wondering if the procedures would be doable in your practice, know that these researchers focused on making the treatment as practical as possible (!). Thirteen preschoolers with phonological disorders participated in therapy in pairs for two hour-long sessions per week for 8 months.

Note: The study also looked at a couple different intervention approaches, but we aren’t focusing on that aspect for the review, mostly since there didn’t turn out to be much difference between the two. Check out Table 2 in the paper for a summary of the treatment techniques, if you’re interested!

Back to the outcome measures. The authors focused mainly on PCC, which is calculated like so:

PCC = (number of consonants correct / total number of consonants) x 100

It’s important to know that clinicians and researchers have calculated PCC using both conversational samples and words lists. The authors used both of these PCCs, and added a few extra measures to look specifically at Shriberg’s (1993) “late 8” consonants. There were six total outcome measures—three based on a conversation sample and three taken using a word list:

  • Percent of all consonants correct (PCC), list and conversation
  • Percent of all late/difficult consonants correct (L/D PCC), list and conversation
  • Number of late/difficult consonants present in the sample, list and conversation

The researchers found that all of the measures were sensitive to changes in the preschoolers’ speech sound usage over time. However, they suggest that SLPs use PCC-List and L/D PCC-List. Here’s why: 1) other measures looking at late/difficult phonemes had floor effects and 2) the pre-and post-treatment data obtained from PCC-Conv reflected small numerical differences, even though students made gains.

SLPs who support preschoolers can use the list in Appendix A when measuring PCC-List, keeping in mind that the researchers used photographs and colored drawings when obtaining speech samples from children in the study. The authors also recommend supplementing this data collection with an intelligibility measure like this.

How might these methods improve your progress monitoring for students with phonological disorder?

Smit, A. B., Brumbaugh, K. M., Weltsch, B., & Hilgers, M. (2018). Treatment of phonological disorder: A feasibility study with focus on outcome measures. American Journal of Speech-Language Pathology. Advance online publication. doi:10.1044/2017_AJSLP-16-0225.