Learning Geometry emphasizes exploring different representations such as virtual manipulatives, written math formulas, and verbal explanations, which help students build mathematical concepts and develop critical thinking. Student's performance in G.C.E (O/L) examination in Sri Lanka for the Geometry component is at a very low level. This study aims to identify the difficulties of learning Geometry at Grade 11 and provide some suggestions for overcoming these issues using active based learning. This study uses a quantitative survey, a diagnostic test, and a teaching experiment conducted with randomly selected three hundred students from grade 11students and 35 mathematics teachers from 42 schools in Vadamarachchi education zone Sri Lanka. Questionnaires were used to collect data from the teachers and the students. The diagnostic test was also used to collect data from the students. Forty students were selected for the teaching experiment based on diagnostic test results and divided into two equally talented groups using a rubric. The teaching experiment was done to test the effectiveness of activity-based teaching methods in teaching Geometry. Findings from the study revealed that students had greater difficulties in learning Geometry such as drawing diagrams for a given geometric problem and applying more than one theorem to solve a given Geometry problem. Furthermore, Students' disinterest in the Geometry component and their family background affects their Geometry learning. Additionally, results from the teaching experiment indicate that the student-based learning approaches are more effective than conventional methods for teaching Geometry.