For students across the United States, the start of the school year means meeting new teachers and classmates. Some will also say hello to their new class pets. Many teachers keep fish, hamsters, and other animals in their classrooms.

Teachers say students learn important lessons from the animals. According to the American Humane organization, more than 70 percent of teachers who have classroom pets say the animals help students learn responsibility. Research also shows that classroom pets can reduce stress. 

“Pets are great companions and can comfort kids who are having a bad day,” says Lisa Robbins. She works for a group called Pets in the Classroom. 

But others think pets should be expelled from classrooms. In January, the Durango School District in Colorado began enforcing a no-pet policy. Now animals can be brought into Durango schools for certain lessons, but they can’t stay. Officials were worried that animals might create problems for kids with allergies. They were also concerned about the animals getting proper care.

“Who will ensure that they are protected and fed over weekends and during school breaks?” asks Andrew Burns, the chief operations officer for the Durango district.