April 15 2020
Steps by Step process
Step 1:
Login into Office 365 admin account.
Step 2:
Navigate to Microsoft Teams admin center 
Messaging Policies Click Add Create the policies and save, as shown below.
Messaging Policies Click Add Create the policies and save, as shown below.
Screenshot of Student Chat disable policy
Step 3:
Once a new policies are created, go to users select the username Accounts Policies Edit Messaging policies select the newly created policies and click Apply.
select the username Accounts Policies Edit Messaging policies select the newly created policies and click Apply.
Screeshot of the policy to choose
Step 4:
When you’re finished adding new policies for student accounts, the CHAT option should disappear as shown below & you can re-enable the chat feature by reverting the default policies if required.
Screenshot of the end result without chat facility