Education shapes an individual from beginning to end. Education does not merely impart literary ability; it also disciplined behaviors. Education thus is the process of developing the inner abilities. The word achievement is a main student's learning in a particular su bject or a group of subjects William Orora, Fred N. Keraro and Samuel W. Wachanga (2016). Achievement is a measure of how for a particular student has been able to learn and acquire or has benefitted from the learning experiences given to him/her. Achievement is the proficiency of the student assessed by his/her performance in the academic subjects. Present study determine the academic achievement in Biology of 11th class students. In this study, ‘descriptive survey method’ was used. All eleventh class students of Govt. Schools and Private Schools of Sirsa district in Haryana State constitute the population. Purposive stratified random sampling has been used for present study. This study has been conducted on 240 students of 11th class of Sirsa District in Haryana State. In this study Biological achievement test authored by S.C. Gakhar and Himadri was used. Mean, SD, t-ratio were used to interpret the results scientifically and objectively. In this study it is concluded that mean value of Private School students of CBSE is more than Private School students of HBSE regarding academic achievement in Biology. Therefore the academic achievement of Private School students of CBSE is more than Private School students of HBSE, regarding academic achievement in Biology. The mean value of female students of Private Schools of CBSE and HBSE is more than male students of Private Schools of CBSE and HBSE regarding academic achievement in Biology. Therefore the academic achievement of female students of Private Schools of CBSE and HBSE is more than male students of Private Schools of CBSE and HBSE, regarding academic achievement in Biology. The mean value of male students of Private Schools of CBSE is more than male students of Private Schools of HBSE regarding academic achievement in Biology. The mean value of female students of Private Schools of CBSE is more than female students of Private Schools of HBSE regarding academic achievement in Biology. Therefore the academic achievement of female students of Private Schools of CBSE is more than female students of Private Schools of HBSE, regarding academic achievement in Biology.