The purpose of this study was to measure the learning gains for a group of male inmates (n = 124) participating in an adult basic education program in a closed security prison within the southeastern region of the United States. Learning gains were measured for the basic skill areas of reading, math, and language. The number of hours of participation was collected for each inmate participant. The findings of this study found that the inmates had statistically significant (p less than 0.05) mean standardized score gains in reading, math, and language. In addition, this study found that the number of classroom hours of instruction needed for the inmates to increase 1.0 grade-level in reading, math, and language was 118.4 hours, 54.2 hours, and 36.2 hours respectively. The correlation between inmate learning gains and time of participation was not statistically significant. Finally, the personal characteristics of the inmates (age, previous grade-level completed, and time to parole) were not statistically significant predictors of academic achievement. (Contain 6 tables and 2 figures.)