We also found that amongst students who had completed the same lecture course those who had completed the RTR lab performed better on exam questions than those who had not. A class of 182 was randomly assigned to a group of 132 students who did the lab or to a group of 50 who did not. The written exam for the course included questions on relativity that were set and marked by people unassociated with the RTR project. The mean mark out of ten for these questions was 5.4 for the RTR group and 4.6 for the non-RTR group. This is a small but statistically significant difference with a probability of less than 5% of occurring by chance.