Permanent difficulties in learning are investigated in:

Diagnostic evaluation is specifically designed to identify the underlying causes of persistent or permanent learning difficulties. Its purpose is to pinpoint specific areas of weakness and the reasons behind them, allowing for targeted intervention.

• Summative evaluation assesses overall learning at the end of an instructional period, focusing on achievement rather than causes of difficulty.
• Formative evaluation monitors learning progress during instruction to provide ongoing feedback and adjust teaching, but it doesn't primarily investigate permanent difficulties.
• Therefore, diagnostic evaluation is the correct choice for investigating deep-seated learning issues.