I know how you would like one between two for the pooters etc but if you can't afford it/get someone else to buy/borrow then think outside the box. You mentioned 7 groups for science but I seem to remember a mention of 24 in the class. Let's hypothetically go with the 24 in the class with 5 pooters. Go 1 pooter between 3 means 15 children. This leaves 9 children to collect leaf litter for your trays. Or change this to 1 pooter between 2 making 10 children collecting insects and 14 children collecting litter. You go with with the insect children when your TA goes with the litter debris children. You meet back in the class. Look at what insects you have caught and divide between the 7 trays for closer inspection by your groups of children. As for the trays - they are white trays and can surely be collected as washed food trays. If not try clear food trays. If not try school trays lined with white paper. If not trying baking tins lined with white paper. Have you tried primary resources website - probably preaching to the converted but worth mentioning anyway. Also don't forget cress seeds and cotton wool if you are looking at how plants grow .