Android spinner set default text

I've implemented a spinner into my app. I'm showing a list of schools but I want a default value/prompt so the user knows to select a school. I also want to do this without having to have the prompt as a list item. Any ideas?

Here is my spinner code so far:

selectSchoolSpinner = (Spinner) findViewById(R.id.select_school_spinner);
spinnerSchoolList = new ArrayList<String>();

spinnerSchoolList.add("Please select School"); 
//I don't want to have a prompt like the latter     

ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<String>(this,
    android.R.layout.simple_spinner_item, spinnerSchoolList);

spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

selectSchoolSpinner.setAdapter(spinnerAdapter);