For the characterisation of materials, the aeronautical industry accesses the expertise and the support of independent test laboratories. For the execution of characterisation tests of materials it is important that the test laboratory can fulfil the requirements of the testing expertly and continuously improves knowledge related to the tests. Quality systems are very helpful in this respect. One element of quality management systems is the internal round robin tests. This paper presents a procedure of teaching new operators to carry out tests. In addition, this article underlines how the importance of interlaboratory tests for finding and eliminating mistakes made by new operators. The analysis was performed for tensile tests. This test enables the assessment of operators and significantly improves the quality of tests.