First, you'll need to decide on two aspects of pre-school you want to compare and contrast. No one can do that for you.
Then you will need to research and research until you get all the information you need about the two facets of your topic.
Re-researching may continue into the planning process.
Whenever you are writing a comparison/contrast paper (paragraph, essay, research paper), you need to plan it out very carefully on paper first.
1. Write all the information about one of your topics on one page.
2. Write all the information about the other topic on another page.
3. Then put them together in this order:
2. All about topic A
~~~2A. detail 1
~~~2B. detail 2
~~~2C. detail 3
~~~2D. detail 4
~~~2E. detail 5
3. All about topic B
~~~3A. detail 1
~~~3B. detail 2
~~~3C. detail 3
~~~3D. detail 4
~~~3E. detail 5
The number of details for each topic will vary depending on your main points. I would include comparisons (how they are similar) in the introduction and conclusion, but sections 2 and 3 and all those details will be stating and explaining how they are different.
There are two recognized patterns for writing comparison/contrast papers. One is casually referred to as "zig-zag,” but can be very confusing for the reader if you don’t use transitions effectively. The other is topic-by-topic (which is what I've outlined above) and is much easier for the reader to follow.
See http://leo.stcloudstate.edu/acadwrite/comparcontrast.html for further help with comparison/contrast writing.
Once you have organized your information, please re-post if you’d like feedback from someone here.