If VAT (Sales Tax) does not apply, set rate to 0.

Where VAT (Sales Tax) applies, set the tax rate as 0% but the inclusive rate as required eg. 5%.
Class provides "merge" fields for both the inclusive VAT value and rate.
The invoice will show the total value (including VAT) and a separate column will show the VAT amount/rate, if required.

Note: The VAT (Sales Tax) amount will be extracted (in total) from the posted sales value. VAT (Sales Tax) in the above example is not recorded separately.

If VAT is shown as a Tax rate (see above), then the VAT will be added to the value of the invoice.
This is an unusual treatment for a language school, as values are normally shown inclusive of VAT (Sales Tax).