radio_button_tag(:school_type, type, '')

=> "<input checked=\"checked\" id=\"school_type_online\"
name=\"school_type\" type=\"radio\" value=\"online\" />"

Note that I passed it a default value of '' and it spit out that it that
my radio button was checked. Is that right?

The third parameter is whether or not the radio is checked. false and nil are false in ruby, everything else (including an empty string) is true, and so your radio button gets checked.