Do I have to pay all my loans or can I concentrate on just one?

Many student loan companies will give you the option to specify where your payments go or to reapply a payment once it is made.  So if you have the option does this mean you can just put all of one payment towards the loan with the highest interest rate to pay it off fastest?

Not if you are in repayment.

Every loan you have has its own individual payment.  So if you have 4 loans that are for $25.00 each, even if you only have to make one $100.00 payment to your servicer you still have to make sure each of the $25.00 payments are made.

However there are times you can use the specify payment function.

For example lets say your account is paid ahead and those loans were already satisfied.  Or your payment is $300.00, you pay $400.00 and you want to dictate where those funds go.

The most common one would be if you are not in repayment (for example grace, forbearance, deferment etc.)

However overall the key is to make sure your smaller loans are satisfied before you turn your attention to paying more on a loan.