What are you doing with 'Lesson 3' ? If you inject this into a query without escaping, your query will fail.
A better url would be...
No quotes, no spaces. You can convert the GET class_name by replacing all - with spaces before using. Spaces and quotes in urls are weird like I stated. Better still store the resource as Lesson-3 (or Lesson3 or Lesson_3) in the first place