The general experience in teaching flying is that a wide range of the population can learn to do it in a short period. To this point we have been discussing learning factors and techniques for teaching flying in detail with the end goal being efficiency and producing a superior product. For gliders, almost any organized flight training program can get students to the solo in about 40 flights encompassing 10 hours of flight instruction. In a concentrated course, with more directed instruction, this stage can be reached in as few as 25 flights or about 8 hours of flight time. However, it can take some students longer to have the confidence and judgement to solo this quickly.
These training schedules, also pre-supposes that your students are learning on low-energy aircraft, such as the Blanik, K13, SGS233 and the like. Much of the training community likes the more modern aircraft such as the G103, or the K21, however the simple facts are you can easily double the training time to solo in these gliders. The very qualities of responsiveness and efficient energy translation of these aircraft prized by pilots, actually get in the way of students going solo quickly. Students inevitably take longer to develop an appreciation for the feel part of flying and make control mistakes. These mistakes in the older aircraft usually are of little consequence, but the same cannot be said of them in a K21. The result is that training programs using aircraft such as the K21 typically require 60 flights minimum to solo.
Of course some students take longer regardless of the equipment used, and some never quite make it. While students may not complete their training for many reasons, in terms of skill, however, a good estimate is that only about 1 in 40 lack the crucial skills. Student progress then is more influenced by motivation and other factors rather than the skill level of the average student.