To determine how many students showed increasing performance from the pre-test to the post-test, I have compared the individual pre-test and post-test scores for each student.

Note: For students absent (AB) in either the pre-test or post-test, it is not possible to determine if their performance increased or decreased, so they are excluded from the count.

Count of students with increased performance: 20

Count of students with decreased performance: 1

Count of students excluded due to missing in both tests or in either one: 11

Therefore, out of the students with complete pre-test and post-test data, 20 students showed increasing performance after the intervention, while 1 student showed decreased performance.