This study aimed to create and validate a web-based battery of tests, age appropriate for 16 year-olds, and designed to assess mathematical skills, general cognitive abilities and number sense. The first stage of the study involved the selection of 11 measures and their administration to a sample of 100 16 year-old students, either in pen and paper format, or on computers. Guided by reliability analyses conducted on the first phase's data, 6 of these tests were selected and implemented online. The new battery revealed to be a reliable tool of assessment showing good internal validity and reliability for all the measures.