Assessment for learning is an approach to assessment that focuses on the ongoing process of gathering and interpreting evidence of student learning. It is designed to provide feedback to both students and teachers to guide and support the learning process. Option A, sharing exemplars at different levels of success according to certain criteria, is the correct answer because it aligns with the principles of assessment for learning.

Here is a detailed explanation of why option A is the correct answer:

1. Sharing exemplars:
- In assessment for learning, teachers provide students with examples or exemplars of different levels of success.
- These exemplars demonstrate what successful work looks like and provide students with a clear understanding of the criteria and expectations.
- By sharing exemplars, students can compare their own work to the examples and identify areas of strength and areas for improvement.

2. Different levels of success:
- Exemplars are shared at different levels of success to provide a range of examples.
- This allows students to see how their work compares to both high-quality work and work that may need improvement.
- By seeing examples of different levels of success, students can gain a better understanding of how to improve their own work and set realistic goals for their learning.

3. According to certain criteria:
- Exemplars are shared based on specific criteria or standards that students are expected to meet.
- These criteria may be related to content knowledge, skills, or other learning outcomes.
- By sharing exemplars that align with the criteria, students can better understand what is expected of them and how to meet those expectations.

Assessment for learning focuses on using assessment as a tool for learning, rather than simply assigning grades or marks. It emphasizes the importance of providing timely and constructive feedback to students to guide their learning process. Sharing exemplars at different levels of success according to certain criteria is a key strategy in assessment for learning as it helps students understand the expectations and criteria for success, and provides them with concrete examples to guide their own learning and improvement.