When adding the suffix -ed to make a past tense, you might assume it always makes an /id/ sound, but in reality there are three sounds of -ed. It can say /id/ as in wanted. It can also make the /t/ sound as in looked. The third sound is /d/ as in called. When we converse we don’t think about the different sounds we make when talking in past tense, but we need to when we convert it to writing.
It may seem arbitrary when we say -ed one way or another but there is actually a very systematic way we say each of these sounds. The /id/ comes out when the end of a word is /t/ or /d/. I call them the Ted words, because they are either t or d.
The /t/ sound comes from the sounds /s/, /k/, /p/, /f/, /sh/, /ch/, /x/, unvoiced /th/. These are sounds that are called “unvoiced”. These sounds are said in our mouth and not in our throat. With words that end with these sounds, we naturally say the /t/ sound when making something past tense with -ed. I teach my kids this sentence to help them remember the unvoiced sounds. Skip has the fish & chex. Remember that these are sounds are not letters. So, if you have a soft c that says /s/, or if you have the unusual gh with the /f/ sound, you would say the /t/ sound – fenced, laughed.
The /d/ sound comes from the voiced sounds, essentially all the other sounds not listed above. Instead of listing off 11 sounds, I usually just teach the first two and by default all the others will be /d/ sound.
The importance of teaching the 3 sounds of -ed, is mainly for spelling. Spelling -ed is not the complicated piece, it is distinguishing it from words that end in: -pt, -ct, -ft, -st, -nd, -rd, -ld. It is only these 7 endings in which older students seem to get confused. You will see words spelled: malld, reflecked. When a student is spelling in this manner, this is the concept that has eluded them.
It’s important for them to understand the concept of “passed tense”, but what throws a wrench in things with words like swept. Although there are only a few past tense exceptions, those spelling patterns can be taught as well. I find that this concept plagues the older student often as words get longer. They like the fact that it is only 7 endings to watch out for. Giving older students hope for spelling is so important. With exposure to the explicit rules and review they can master this concept!