Doctoral students from across South Africa are joining the struggle for free education. Their weapon: their knowledge.Their target: thousands of protesting students who have taken to the streets to demand free education.The PhD students have, like their fellow students, put out the word on social media, offering their services at night for free.Wits PhD student Lindsay Donaldson said: "It is not about us. It is about ensuring that those who are out on the street after winning their battle for a free education are not once again excluded, this time academically."Donaldson, who is completing a doctorate in nuclear structure physics, said the tutors feared the university would keep its examination schedule, despite the protests."If this happens a lot of students will be at risk with their studies. It is no good for the students to avoid financial exclusion only to be subsequently excluded [from tertiary education] because of poor academic performance."She said through social media she and other doctoral students across South Africa were offering their services."There are five of us from Wits making ourselves available to students, who we have heard have arranged night-study sessions."Tutoring was for students in chemistry, physics, computer programming and computational and applied maths, she said...