In the past I have done the same - cutting up pizzas for fractions and measuring out rice for activities with mass - but in reflection I think I have a problem with using food this way.
Here are some of my reasons:
Not sure if your school is the same as mine but we have a number of students with food-related allergies. Many of these allergies are life-threatening. If I was to bring in a cake to cut up for fractions work, it would need to be nut free, lactose free, gluten free and egg free. Or I could exclude the kids who had these allergies from the lesson. I don't think this would be fair - or safe.
2. Religion and Culture
We are currently in the middle of Ramadan in Australia. It would be pretty insensitive of me if I was to bring food into my classroom to use for maths. There are children who would not be able to participate and it would put them in a difficult position. There are other cultures and religions that have specific requirements with food preparation and handling that I could inadvertently offend by using food in my lessons.
3. World Hunger
There are people around the world who do not get enough food to eat each day. Can I ethically justify using food as a maths resource while they are starving? I want the children I teach to have an awareness of their global responsibilities - by respecting the needs of others' and by not trivialising significant world problems.
My classroom is just that - a classroom. It isn't a food preparation area and hygiene standards are not what would be required in a restaurant kitchen. I don't want the responsibility for any sick children who cross-infect others as a part of a maths lesson.
I've mentioned my feelings about sugar elsewhere in this blog. I don't think children need to be given more sugar by teachers who are using jelly beans or Skittles as part of a maths lesson. I need to be making responsible choices on behalf of the children that I teach.
6. There are other ways
Be creative - think of another resource that you can use to demonstrate and practice the skill. Coloured plastic counters may not taste as good as sugar covered treats, but what the kids really crave is affirmation and recognition from YOU - the teacher. If they only want you for your chocolate, then that's a pretty shallow relationship.
Am I a hypocrite?
I did write about a lesson we did with our buddies last term when we cooked muffins to teach measurement. Wasn't that food? Wasn't that what you just said not to do?
Well, yes and no.
The purpose of lesson was social as well as mathematical. We were having a celebration party to end the term and thought we could prepare the food as a bonding activity with our buddies.
The ELC has a kitchen that we used - it wasn't a classroom as such - so we were able to keep things pretty clean.
Yes - we did consider children with special dietary needs. We were able to accommodate them with variations in the recipe. The boy with the most critical allergies was provided with an alternative food by his mother but he was able to participate in some of the measuring and mixing of the muffins.
We didn't waste the food or play with it - it was part of our end of term party.