If you want to deal with late students, first of all, you need to find the real reasons of it. If you start to punish with finding the real roots of reasons behind this, you are doing big mistake. Punishment may help them to make this bad habit.
There are lots of reasons behind this.
1. Drivers may be the issue
There may be transport delay issue. So, solve it first. Some area of India, drivers of school bus or vehicle are lazy. Due to this, some students come late. Teachers do not know this issue. So, after good inquiry from students, they come to know this issue. After this, they try to best to solve this issue.
2. Parents may be the issue
Some parents get up late on every morning. Due to this, students will get up late. So, they will go to school at later time. So, as a teacher, you should motivate the parent to get up earning in the morning.
3. Fear of teacher will be an extra issue
Sometime, more strictness will bear the fear in the innocence mind of students. So, teachers need to change their behavior with students.
4. Laziness is student's issue
Some students may be lazy. So, they walk slow and reach late at school gate. So, teacher should motivate them to do hard work.
Like this, you can make the list of issue of students. Now, you try to solve each issue one by one by your intelligence. You need to increase your intelligence for solving this issue, late students problem will automatically be solved.
a) You should give the reward to every student who will follow your rules.
b) You can tell the importance of punctuality to your student.