Drum Publications has written a guide on how to the pronounce the Karen alphabet.
Phonetics is always at the top of the list for teaching language. The references below may be useful to you.
The Karen alphabet (using Burmese script), and spelling of words was developed in the early 1860s by English missionaries. Since each vowel and consonant sound has one, and only one symbol, it makes an excellent phonetic transcription tool for teaching adult Karen students the sounds of English letters. The only immediate problem being that some adult Karen ESL students can not read or write Karen. Children were taught to read and write Karen in refugee camp schools. Young refugee children immigrated before they went to school and therefore they cannot read or write Karen, but unlike their parents it doesn’t matter since they are being taught English in public schools.