Hide Button based on a specific picklist value

Question

I have the following VisualForce page. I have a picklist with the name Tip_studija__c. The pickist can have the values 'redni' or 'izredni'. I want to achieve the following: when I choose the value 'izredni' the button shows and when I click on the value 'redni' the button hides. That button is labeled as Samoplacnik.

My code does not achieve this and I do not know where is the problem.

<apex:page controller="CustomStudentController">
<apex:form id="form1">
  <apex:pageBlock id="mainSection" title="Nov Student">
     <apex:pageBlockSection columns="1">
        <apex:inputField value="{!Student.Name}"/>
        <apex:inputField value="{!Student.Priimek__c}"/>
        <apex:inputField value="{!Student.Letnik__c}"/>
        <apex:inputField value="{!Student.Naslov__c}"/>
        <apex:inputField value="{!Student.Datum_rojstva__c}"/>
        <apex:inputField value="{!Student.Naziv_fakultete__c}"/>
        <apex:inputField value="{!Student.Studijski_program__c}"/>
        <apex:inputField value="{!Student.Tip_studija__c}" rendered="{!IF(Student.Tip_studija__c == 'izredni', false, true )}">
            <apex:actionSupport event="onchange" rerender="placnik" />
        </apex:inputField>
        <apex:selectcheckboxes id="btnSpl" layout="pagedirection">
           <apex:selectOption id="Placnik" itemValue="Samoplacnik" itemLabel="Samoplacnik" />
        </apex:selectcheckboxes>
        <apex:pageBlock id="vsi" title="Vsi studenti">
           <apex:pageBlockTable value="{!students}" var="wrapper">
              <apex:column value="{!wrapper.Name}"/>
              <apex:column value="{!wrapper.Priimek__c}"/>
              <apex:column value="{!wrapper.Naslov__c}"/>
              <apex:column value="{!wrapper.Datum_rojstva__c}"/>
              <apex:column value="{!wrapper.Naziv_fakultete__c}"/>
              <apex:column value="{!wrapper.Studijski_program__c}"/>
              <apex:column value="{!wrapper.Letnik__c}"/>
              <apex:column value="{!wrapper.Tip_studija__c}"/>
              <apex:column > 
        <apex:commandButton action="{!deleteStudentRecordById}" value="del" reRender="mainSection"> 
        <apex:param name="studentId" value="{!wrapper.id}"/> 
        </apex:commandButton> 
        </apex:column> 
        </apex:pageBlockTable>
       </apex:pageBlock>
        <apex:commandButton action="{!SaveRecord}" value="Save" id="theButton" reRender="mainSection"/>
    </apex:pageBlockSection>
   </apex:pageBlock>
  </apex:form>
 </apex:page>

Answer 1

1. Try enclosing the button code in a outputpanel and try to rerender that.

2. If it still doesn't work, check if you have any required fields on the page, which might be preventing the page to rerender due to invalid form. If this is the case, you will have to enclose the picklist and button code within a actionRegion

3. Also, add 'apex:pageMessages' tag at the top of the page to check for any errors.