Final answer:
Useful feedback after a formative assessment should be detailed, specific, and constructive, focusing on reinforcing, guiding, and encouraging students to apply concepts in practice.
Step-by-step explanation:
The most useful feedback for a student who has completed a formative assessment would be specific, detailed, and aimed at reinforcing concepts while guiding improvement. An example of constructive feedback might include an explanation of any misconceptions demonstrated in the student's answers, praise for concepts well understood, and suggestions for skills or knowledge areas that need further development. The feedback should also encourage students to apply what they have learned in practical situations, which can deepen their understanding and ensure they are prepared for summative assessments.