The self-report version of the Strengths and Difficulties Questionnaire is widely used in clinical and research settings. However, the measure’s suitability for younger adolescents has recently been called into question by readability analysis. To provide further insight into the age-appropriateness of the self-report Strengths and Difficulties Questionnaire, readability was assessed at the item level alongside consideration of item quality criteria, its factor structure was analyzed, and measurement invariance between adolescents in Year 7 (age 11-12 years) versus Year 9 (age 13-15 years) was tested. The measure showed a wide range of reading ages, and the theorized factor structure was unacceptable. Measurement invariance was therefore considered for a flexible exploratory structural equation model, and no evidence of differences between age groups was found. Suggestions are made for the measure’s revision based on these findings.