Environmental education (EE) practitioners struggle to consistently and rigorously evaluate their programs, particularly when little time is available for evaluation. Since environmental literacy (EL) is the goal of environmental education, a very short EL instrument -- amenable to use when longer tests are not practical for practitioners -- would address an important EE need. We describe the development and validation of the Environmental Literacy Instrument for Adolescents (ELI-A) that is short enough for use in field applications (i.e. 5-15 min) and measures four domains of environmental literacy (ecological knowledge, hope, cognitive skills, behaviour). Factor analysis, item response theory, and concurrent validity tests were used in the validation process. Structural equation modelling supported the fit between the ELI-A and prevailing EL frameworks. The results support a valid and reliable instrument that is short enough for practical use but comprehensive in measuring four primary components of EL. This instrument could help fulfil the call to evaluate EE programming in both formal and informal settings.