|This study investigated the effects of teaching vocabulary words in thematically versus randomly grouped sets in the context of various forms of rich vocabulary instruction. A group of 62 fourth graders was taught 49 selected words. There were 19 students in the Frayer control group, 21 students in the Rich mixed group, and 21 in the Rich thematic group. Each group received a form of rich vocabulary instruction. The Rich mixed group received instruction that focused on student friendly definitions, examples and non-examples, text reading, and student discussion about word use. The Rich thematic group received the same instruction. The Frayer control group's instruction was based on finding synonyms and antonyms and using each word in a sentence. Statistical analysis revealed that learning words in thematically grouped sets in the context of rich vocabulary instruction did not yield a statistically significant difference over learning words in a randomly grouped set in the context of rich vocabulary instruction, although students who learned words in thematically grouped sets did slightly better. All three groups showed significant growth from pretest to posttest with rich instruction and words taught randomly and thematically. The major finding was that the Rich themaic instruction group had scored that were statistically significantly greater than the combined random instruction group. The results indicated that teaching words in randomly grouped and thematically grouped sets is effective when both approaches are used in the context of rich vocabulary instruction. These results contradict findings from other studies indicating that presenting words in related sets causes interference with learning words. This study adds evidence to the body of research literature showing that rich vocabulary instuction with word learning activities in which students make connections to other words and concepts does facilitate vocabulary growth. The conclusion is that rich vocabulary instruction should be a part of vocabulary instruction. The added component of grouping words for study into thematic groups can be an effective approach to teaching vocabulary words. However, the same results might be achieved without thematically grouping words. The main factor in effective vocabulary instruction is that the instruction be rich.