How does class 1 entry work at Bethel Senitt High School in Karmanghat?

We're widening the list for our son's class 1 next year, and Bethel Senitt High School came up through a colleague who grew up on that side of the city. He's at an ICSE preschool in Tellapur at the moment. Before we visit, I'd like to understand the process. Is there an interaction or assessment for class 1 joiners, and roughly when do forms usually open? I'd also be interested to hear from anyone whose child moved from an ICSE preschool into State Board class 1, and whether the change in reading and writing expectations was noticeable.