I teach beginner and intermediate kids. Beginner classes are 30 mins and Intermediate are 45 mins. Generally, i have some idea beforehand what im going to focus on for class. I tend to spend about 10-15 mins with warmups, followed by the main lesson, and end with about 5 mins of a game. As a rule, all students must stretch out before class starts. Occasionally i will teach them stretches as their main lesson in the beginner class, and i usually ask the more experianced students to help the newer ones. However, i always teach the new student some main stretches first... As far as "winging it", ive been teaching for 4 years and i wing it 99% of the time. At first i used to have a structured plan, but i found that once i got in front of the class, the plan was never followed, as i taught more with the flow of the students. As far as i know, none of the instructors at my school uses a lesson plan. I like it that way, i think it makes the class more flexible to the particular students needs. On another note...I also teach the 3-6 year old class With them i prefer to constantly change up whats going on, and never spend more then 5 mins doing any specific thing. However, as they get more and more acustomed to the dojo environment, ive found that i can teach their lessons with the same structure as the older students.