I particularly like this activity: What is the best way through the maze to collect as much money as possible? The link is here.
The quality of the resources is superb: in the ZIP file is a flash program that can be loaded with a web browser. Then children can play with the puzzle like a game. This will be very motivating: the activity then leads children in to recording their mathematical ideas, developing a systematic approach, and explaining their understanding.
There are excellent progression criteria which are written for children, so they can self-assess. There are examples of children's work to show the different levels. Look at all these great teacher notes and support you can download:
This pupil (A) is completing the task at a basic level. We can assess him according to these categories:
Let's look at some high achievement on this task:
I won't fully analyse this child's work, but you can see they have represented the problem in calculations (but not in algebra), they have analaysed using a systematic approach, and have extended the problem to different sized mazes: they have a much higher level of understanding being able to follow a systematic approach for this much more complex problem. They have skills in interpreting and evaluating, by writing down generalizations, explaining them, and testing them. They've communicated and reflected on their learning.
In both examples, it's clear that written work provides some assessment information, but it's of limited use in assessing how well the children can interpret and evaluate the solutions, and how skilled they are at communicating and reflecting on their work. There are two obvious solutions, both with merits:
1. Verbal feedback through discussion with the teacher. Whilst this is extremely useful as a learning strategy in itself, there's clearly practical limitations.
2. Self-assessment and peer-assessment by the students: The main challenge here is to ensure the children have the skills to do this effectively. Not only do they need to be practiced in the language and structure of a constructive conversation, they need to be very clear about what they are assessing. The Nuffield student-friendly progression tables are a great start here, but it's really up to the teacher to ensure the children clearly understand the broad aims of the task and the parts of assessment. There's great potential here for students to be reflective and empowered learners. If as educators we spent our whole careers improving teaching in this area alone, it wouldn't be time wasted!