Conditional Discounting

Hi,

From what I understand the "number of weeks" on your website is actually the "quantity" of the product in the cart.
And the "english courses" are only some of the products on your website, as you're also selling other things, which, from what I understand of your message, won't get the discount.
So, one solution I can see is to edit these products, and add extra prices with start / end dates and a "minimum quantity" and a reduced price.
While this is the simplest solution, it's also the more labor intensive, as you'll have to add a few prices for each product.

Another solution I can see is to create a coupon on the category of these products (or create a new category and add it as a second category for all of the products you want the discount to apply) via the menu Orders>Coupons. There, you can use the "Product quantity from" setting to set the 1 to 12 range, etc and then you can select the category in the "category" setting, you want to turn on the "Product quantity from" and the "Coupon percentage applies to product only" settings, fill in the end and start dates, and the percentage, and it will do it automatically.
Note however, that in this case, if someone purchase 10 weeks of english course 1, and 5 weeks of english course 2, the 20% coupon will apply for the sum of the amount of both products.