It is with great pleasure that Simon and I would like to announce a new release of the STACK CAA system.

STACK is an open source computer aided assessment system for mathematics. The use of the computer algebra system Maxima provides a suite of tools with which a teacher may establish mathematical properties of the student's final answer. On the basis of these properties outcomes are assigned in the form of a numerical mark (including partial credit as appropriate), text based feedback to the student and a "note" for later analysis. These three outcomes correspond broadly to the

summative, formative and evaluative purposes of assessment. This is much more sophisticated than multiple choice formats, but falls short of being able to automatically assess chains of related mathematical expressions, i.e. assessing a full "worked solution".

We have changed the way STACK is documented, and now documentation (including installation instructions) are online at

We have installed a (temporary) demonstration server.

http://stack.bham.ac.uk/new-moodle/

and we would like to invite you to have a first look. Please be gentle with this, as this is the first occasion on which we have tested STACK with real people. Please do be patient if this falls over. Please contribute to the forum on that Moodle with your thoughts and report anything which is out of order.

This is a new release, and I'm painfully aware of the number of bugs we still have to fix. However, we have reached a point where we would like some comments, and of course help in future development.

You are very welcome to create an account on our new Moodle version to look at some sample questions. Some questions are randomly generated, and you may repeat quizzes to get new versions. We haven't deployed very large ranges of random questions, so don't be surprised if you recognize a couple on

each new quiz.

The new features we have added are as follows.

(1) The display of mathematics is now client side using Moodle's JSMath filter. This will increase, we hope, accessibility and reduces processing load on the server.

(2) STACK is now fully integrated into Moodle, including question authoring.

(3) Mathematical questions now have built-in test cases support. Similar to unit tests in software development, these allow the question author to verify the outcome of items for student answers in terms of any random parameters. By including this information within the item, the author can test questions and furthermore, when the question is shared, other teachers can more easily understand the intensions of the original author.

(4) STACK now optimizes its use of computer algebra with a dynamic caching layer. This shifts future optimization and scaling work to database design where it can more effectively be addressed. The record of attempts operates at this layer,

which can be analyzed later for statistical analysis of a question.

You will not be able to see (2)-(4) in action on this demo server as only question authors can see this!

There are some important bugs which we are going to work on immediately. We are using the sourceforge bug tracker for these and also to let people propose features

https://sourceforge.net/projects/stack

Some interaction elements don't work in Moodle, so these have not been included in the demos online. This includes dragmath. We intend to put all these features back in the near future.

There are also some serious problems with the Opaque protocol. It has been quite interesting to me how difficult it proved to be to separate questions from quizzes. To be honest, I really underestimated how difficult this was. This realization has

caused us some serious delays and headaches!

One option is to create a completely new STACK block and not use Moodle's quiz at all. I'd welcome your comments, but really don't want to write my own quiz management system!

In particular

(1) we can't distinguish between genuinely new attempts, and calls to reconstruct a version for a student. This causes us problems in recording the number of attempts which have been made at a question. (Only a problem when generating statistics, so this shouldn't cause problems for students)

(2) I'd like to be able to restrict full worked solutions to be available only after a due date. But currently there is no way to link such time based events into Opaque. So, the only options are

- not to have worked solutions!

- to let the student ask for it anytime.

This is not very satisfactory, but we intend to change how this works soon.

(3) Some features don't work in Moodle, including DragMath input and the Matrix interaction elements. These are bugs we will fix over the next few weeks I hope.

I hope the STACK system is a useful additional question type for Moodle.

Comments and contributions are very welcome at all levels, from those who like to author interesting questions for student through to people who like to work with the raw code itself.

Chris (& Simon).