A lesson is considered to be a class observation, whatever is appropriate for the group of students involved. For example, a kindergarten class observation could be shorter than a middle school math lesson. Walk throughs are intended to be approximately fifteen minutes in length and should be at a time when instruction is taking place. Within the TIGER model, walk throughs are primarily unannounced. However, adaptations can be made as long as the minimum amount of time, number of observations, and percentage of announced vs. unannounced visits occur as required by the Tennessee State Board of Education policy.