How do I display entries from multiple entry types?
You can set the ElementCriteriaModel's type parameter to multiple values by passing it an array of entry type slugs:

{% set teachers = craft.entries.section('teacher').type(['teacher', 'demoTeacher']) %}


Use the type property on the entry model to access its entry type in your conditional (also see this list for other available properties).

{% for teacher in teachers %}

    {{ teacher.title }}

    {% if teacher.type == 'demoTeacher' %}
        ...
    {% endif %}

{% endfor %}