How to set a dynamic checkbox as true/false

im a bit wondered..

I have multiple checkboxes which will be generated at runtime with the name chk_WoK1, chk_WoK2, Chk_WoK3.

I thought I can set them like this:

this.Controls["chk_WoK1"].Checked = true;

but this seems not working. I used this because it worked already for Label Objects.

Can anybody tell me another method to assign them?