Measuring Intelligibility for Meaningful Speech Progress

With progress reporting periods approaching for SLPs across the country, there’s no better time to shine a spotlight on intelligibility. 

Parents, teachers and even SLPs can become laser focused on accuracy and percentages as students settle into their speech therapy routines. Intelligibility—how effectively a person can be understood by others—offers a fuller picture of a student’s progress and may be easier to measure than you think!

Looking Beyond the Numbers

While tracking articulation accuracy is fundamental to data collection, it doesn't always translate directly to improvements in the real world. A student might achieve 90% accuracy with a target sound in structured therapy tasks but struggle to be understood during classroom discussions or conversations on the playground.

Intelligibility is influenced by numerous factors beyond isolated sound production:

• Speech rate and rhythm
• Prosody and intonation
• Word and sentence complexity
• Communication context

When we focus exclusively on accuracy percentages for individual sounds, we risk missing the bigger picture of how effectively a child is communicating in daily life.

Measuring What Matters

To better capture and track intelligibility, speech-language pathologists can employ these metrics that better reflect real-world communication:

Percent Consonants Correct (PCC)

PCC measures the proportion of consonants a child produces correctly in a speech sample.

How to calculate:

1. Collect a speech sample in a motivating context (conversation, story retelling, or play)
2. Count the total number of consonants attempted (the first 100 can suffice in a pinch!)
3. Count how many consonants were produced correctly
4. Divide the number of correct consonants by total consonants and multiply by 100

For example: If a child attempts 100 consonants and produces 65 correctly, their PCC is 65%.

Percent Words Correct (PWC)

PWC evaluates how many complete words are produced accurately in connected speech.

How to calculate:

1. Collect a speech sample in a motivating environment
2. Count the total number of words attempted (typically 50-100 words)
3. Count how many words were produced entirely correctly
4. Divide correct words by total words and multiply by 100

For example: If a child attempts 100 words and produces 73 entirely correctly, their PWC is 73%.

These metrics provide quantifiable data that reflect a child's functional communication abilities and can be used to track progress over time. In fact, research shows PCC and PWC have stronger correlations to judgements of intelligibility when compared with big box tests of speech accuracy!

Shifting the Focus

Consider these approaches to measuring and improving overall intelligibility:

• Utilize functional measures like PCC, PWC and rating scales, such as the Intelligibility in Context Scale, to bolster your progress reports
• Celebrate small wins, including increased class participation and more frequent self-corrections during naturalistic interactions with peers
• Involve the whole team by sharing strategies, such as phonological recasting, or visuals for use in the classroom setting--seek out feedback on what’s working and what could be improved

A Success-Oriented Mindset

Remember that the ultimate goal of speech therapy isn't perfect articulation in controlled settings—it's helping our students become effective, confident communicators across all of their meaningful environments. The next time progress reports creep up on you, consider how these student-focused measures might complement your traditional data and capture your student’s growth.

Author: Teadora Taddeo, CCC-SLP