Both the ou and ow vowel pairs can make the same sound (as in how or out). So how can a student distinguish between the two?

A good rule of thumb is to use ow at the end of a word (or the end of the first part of a compound word, or the end of a word before a suffix is added) and ou if it is not at the end of the word.

One exception to that rule can be found in this level, however: the word down.