Each individual learns at a different rate. According to statistics from the Driving Standards Agency, a learner driver who passes their driving test has had, on average, about 45 hours of professional training combined with 22 hours of private practice. However, this is the national average figure and many pass with far fewer lessons.
Your instructor will provide you with a detailed lesson structure and advise you on your progress using a Driver's Record Card as recommended by the Driving Standards Agency. This will include a guide of what to practise between lessons when you have a car and supervising driver available.