What type of words do Hiebert and Fisher emphasize in their focus on vocabulary development?

Hiebert and Fisher emphasize morphologically related words because these types of words help in understanding the structure and meaning of language more effectively. This approach focuses on how words are formed and how they relate to one another in terms of prefixes, suffixes, and root words. By concentrating on morphological relationships, learners can enhance their vocabulary and comprehension skills, as they are able to decode and derive meanings of unfamiliar words based on their understanding of related words.

For instance, knowing the root word "educate" can help a student understand "education," "educator," and "educational," thereby expanding their vocabulary through the connections established by their morphological components. This strategy promotes deeper learning, as it encourages students to explore the relationships between words, which is not typically achieved through the other options like phonetically irregular words, sight words, or common nouns. These other word types might not provide the same level of insight into the structure and meaning of language, making morphologically related words a more effective focus for vocabulary development.