This study examines the effects of topic interest on the vocabulary learning and retention in third grade students with and without learning disabilities. All students learned 12 unfamiliar vocabulary words in three different vocabulary learning conditions: High-interest topic vocabulary, low-interest topic vocabulary, and vocabulary words without a thematic topic. Harry Potter represented the high-interest topic condition, Ancient Mesopotamia represented the low-interest topic condition, and the No Topic condition consisted of unassociated words without a thematic topic. Two studies were conducted. Both studies used the same methodology, but were conducted on a different student population. The first study involved third grade students without learning disabilities, and the second study compared the same students from the first study to third grade students with learning disabilities. Students without learning disabilities (NLD) who showed high ability in reading comprehension on pretest showed effects of topic interest on vocabulary retention. These students learned vocabulary items better in the high-interest condition, and performed equally in the low-interest topic and No Topic conditions. However, students with low reading comprehension on pretest showed no effect of topic interest on vocabulary retention, and students with learning disabilities (LD) demonstrated a similar lack of effect. The low comprehension students and LD students demonstrated a superior performance on the No Topic condition compared to the high or low-interest condition, suggesting a less clear cut relationship between topic interest and vocabulary learning in these groups. In addition, reading comprehension and word knowledge were significantly correlated in NLD students, and each was significantly correlated with their vocabulary retention. These results give evidence to the strong relationship between reading comprehension and word knowledge, and demonstrate that these two factors play a significant role in students' vocabulary learning. Also, the type of task significantly affected how topic interest impacted students' vocabulary retention. In conclusion, results showed that topic interest can be an important factor in determining how well students retain vocabulary words, but this tends to be true for students with higher reading comprehension ability and is dependent upon the type of task given. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]