There is evidence that we build up words from their meaningful parts, their morphemes, in step-wise fashion, attaching certain affixes before others. Allowing students to discover these processes allows them to think about the meanings of the morphemes, about the parts of speech they attach to, and about the complexity of these processes that we make automatically as native speakers. Understanding that complexity is empowering for native speakers and instructive for non-native speakers of English.
In order to discover the order of morpheme attachment, you need to think about other words that contain those affixes. This process is an important component of the activity; through it, students discover that the affixes behave systematically, that the meanings are consistent, that the parts of speech of the roots and the resulting words are consistent, and that the investigative process is productive.
Example: Determine the order of the affixation of the morphemes for the word rereadable. Label the part of speech of each word along the way. Think about words that contain the morpheme re- and what part of speech re- attaches to. Then, think about words that contain the morpheme -able and what part of speech -able attaches to. This leaves you with only one possible way to build the word.
re + read (Verb) = reread (Verb) + able = rereadable (Adjective)
read (Verb) + able = readable (Adjective) + re = rereadable (Adj)?
Because re- never attaches to adjectives. You can't say rehappy, recurious. Re- only attaches to verbs.
Let's investigate these affixes and some of the words they occur in.
-tion, -able, -ment, -ate
re-, de-, un-
Identify all of the prefixes, suffixes, and roots for each word and determine the order in which they combine. Label the part of speech of each word along the way.