I don't know if there is a simpler code, but here's what I have in case someone else wants to look at it:
<form
method="post"
action="http://webwork.pcc.edu/webwork2/MTHALC20-Dear-S14/U1L3Division/?login_practice_user=true"
enctype="http://webwork.pcc.edu/application/x-www-form-urlencoded"
id="login_form"
target="_blank">
<input name="login_practice_user" type="submit" value="Online Practice" /></form>