Reach a population of 300 citizens without building schools.
This one can be hard, as you'll be expanding when your educated citizens start dying off, which can come as a shock. Make sure not to expand too fast too early.
One of the best strategies for getting this is to create as many tools and coats as you can at the start, while your citizens are the most productive - once your initial citizens die, you will notice how unproductive the new ones are.
Efficiency can help here - make sure that your citizens don't have to walk too far to their jobs.