Students will perform better in the tests when the classroom is at a temperature of 20°C.

Temperature and performance

Lower classroom temperatures and improved air ventilation have been found to improve the learning ability of students. They can help students better their performance by as much as 10 to 20 percent. Lower classroom temperatures and improved air ventilation also help students to perform better at their school exams. Studies have show that students in classrooms with lower temperatures are able to do their work more quickly and make fewer mistakes.

In warm classrooms, students are easily distracted by the discomfort they experience and hence are not able to fully concentrate on their lessons. Warmer temperature tend to make students feel tired and lethargic, as compared to cooler temperatures which help them stay alert. On the other hand, the temperature in the classroom should not be extremely cold.
The temperature in the classroom should be at a level where the students feel comfortable, and are able to better concentrate on the lesson.
 

The hypothesis that students will perform better when the classroom is at a temperature of 20°C is not correct.

Not everyone is comfortable at the same level of temperature in the classroom. What is comfortable for one person may be too warm or too cold for another person. In our experiment, it is possible that some students felt too cold at a temperature of 20°C whilst it is very likely that all of the students were too hot to be able to concentrate effectively at 30°C. Therefore, it is better to set a lower temperature so that students who find it too cold are able to simply put on  a sweater or jacket to keep themselves warm. This will create a comfortable environment for all
 

The science fair project can also be repeated to compare whether  a change in classroom temperature affects males and females differently.