You can use the onsubmit:false option (see documentation) when wiring up validation which will not validate on submission of the form. And then in your asp:button add an OnClientClick= $(‘#aspnetForm’).valid(); to explicitly check if form is valid.
You could call this the opt-in model, instead of the opt-out described above.
Note, I am also using jquery validation with ASP.NET WebForms. There are some issues to navigate but once you get through them, the user experience is very good.