There is yet another way that speech sound development can be relatively predictable. As I discussed in Speech Sounds and Kids: Part 1, most children will find the following sounds pretty easy to say: vowels, p, m, h, n, w, b, t, d. Children generally go from not producing these sounds at all to, well, producing them. There is no real development of these sounds, per se. They're just suddenly there one day.
But what about the other sounds? The one that are harder, like k, g, f, v, "ng" y, r, l, s, "ch," "sh," j, "th" and "zh"? Some of these sounds don't develop until kids are into their preschool years. Can you imagine if children just left these sounds out of their speech until they were able to say them? We'd never know what kids were saying at all! And yet by age 3, most children are nearly 80% intelligible (if not more). How does this happen? It turns out that children make highly predictable and very systematic errors when they are producing these harder speech sounds-- so predicatable and so systematic, in fact, that most adults are able to "decode" their speech without even knowing they are doing it. It's only when speech sound errors deviate from the norm or are very unpredictable that we really struggle to understand kids-- and this is when speech therapy is often needed.
Without further ado, then, here are the some of the most common "phonological processes" (the systematic and predictable speech sound errors made by children) that many children will use as they develop speech.
- Fronting: Fronting happens when children produce sounds that should be made in the back of their mouth in the front of their mouth instead. Make the sounds /k/ and /g/. Feel how the back of your tongue hits the back of roof of your mouth? Now make the sound /t/ and /d/. Notice how now it's the front of your tongue that hits the front of roof of your mouth? /k/ and /g/ are made in the back of your mouth while /t/ and /d/ are made in the front. Kids frequently "front" /k/ and /g/ by substituting /t/ and /d/. Go becomes doe, key is tee, and cookie might be tuhtee. Fronting usually disappears by the age of three.
- Stopping: Stopping occurs when children stop air from moving continuously out their mouths. Make the sound /f/ and keep it going. Feel how a stream of air flows between your teeth and lips? Now say the /p/ sound. You should notice that there is a small burst of air for the "p" sound rather than a stream of air. You couldn't keep /p/ going if you tried. You can keep the air going, but the /p/ is over with the second you stop the air slightly with your lips and then release it. Stopping occurs when children stop the air from flowing freely. /f/ and /v/ become /p/ and /b/ so that fan becomes "pan" and video becomes "bideo," while /s/ and /z/ become /t/ and /d/ so that sun becomes tun and "zip" becomes "dip." Stopping also affects the sounds "sh" "ch" and "th." Kids usually stop stopping (ha ha) between the ages of 3.5 and 5, depending on the sound they are trying to stop stopping (okay, now I'm just getting punchy).
- Consonant Sequence Reduction (CSR): CSR occurs when children "reduce" (make smaller) a consonant sequence (a series of consonants in a row). They simply leave out one of the consonants, usually the harder one. Stop becomes top, blue becomes boo, and green becomes geen. This tends to get better around 3.5-4 years of age.
- Gliding: Gliding occurs when children make "r" and "l" sounds into "w". "Road" becomes "woad" and "lamp" becomes "wamp." I'm not even going to attempt to explain the mechanics behind this one, mainly because I really hate /r/ sounds. I'm a pretty good speech therapist, but the /r/ sound gets me every time. Anyway. Suffice it to say that this error pattern usually disappears sometime during the school age years (and that if it doesn't, you shouldn't come see me.).
If you are concerned about your child's speech,don't worry too much about trying to figure out what he's doing. Instead, check out the intelligibility guidelines and speech sound development ages in Speech Sounds and Kids: Part 1; if your child doesn't meet the criteria, it's probably easiest to talk to your pediatrician about a referral to a speech therapist. If you're just the curious type, though, step back and listen to your little one-- see if you can pick up on any of the above patterns in his speech. If you hear them, consider yourself well on your way to being an amateur speech-language therapist.
Resource: Clinical Phonology (p. 229), by P. Grunwell, 1987, Gaithersburg, MD: Aspen Systems Corporation