SLPs have tests for pragmatics. E.g., the pragmatics checklist of the CELF-5. The CELF-5 Metalinguistics (for ages 9+). Clinical observations from a speech path.

There are also social skills checklists. SSRS, SRS, etc. You may have some of these if anyone screened him for ASD. Even if they're sub-clinical for ASD, they may be normatively low.

Another option is work skills, which is on many IEPs. This includes work completion, time management, following directions, time on task.

...pronounced like the long vowel and first letter of the alphabet...