You must enable the transaction support (<tx:annotation-driven> or @EnableTransactionManagement) and declare the transactionManager and it should work through the SessionFactory.
You must add @Transactional into your @Repository
With @Transactional in your @Repository Spring is able to apply transactional support into your repository.
Your Student class has no the @javax.persistence.* annotations how @Entity, I am assuming the Mapping Configuration for that class has been defined through XML.