It takes time to build a relationship - your first encounter will just be the start and you are now building trust. Be open, honest and transparent. Be clear about what you can and can't do. Don't overpromise. If you're a small group of elderly people, be honest about that - there are still great opportunities. The smallest act of kindness or goodness can make a great difference. Keep regular contact, but don't become a nuisance. You're there to help, not increase workload. Send words of encouragement and affirmations about the school's work - it can be a tough context where people can feel undervalued. Take it steadily, there is no rush, do what you can and do it well.
Keep discussions in the local church going - inviting others on board as things grow. Keep praying, especially in worship - and value those people who are unable to 'do' things with the school, but have embraced praying for the school as an important part of their discipleship.
Remember, you probably have more resources and assets than you think: Do you have a building which might be able to be used when the school needs space? Are there people with particular skills who could help out, especially in running school clubs? Does the school need things to help deliver their RE curriculum (or even other aspects around spirituality and wellbeing)? Do you have other contacts in the community where you could help build partnerships? Are you able to offer pastoral support to staff - someone who will listen to them? Could you display artwork for the school to share with the community? Do you have finances which could buy spare uniform or shoes for those that can't afford them or lose them?
Keep the conversations open and spot resonance - a need the school has, matched with something you're able to offer.
"It's about relationship with the whole school, not just the children, but staff too, who may also have questions and need support. Be very flexible and understand the culture. Communicate well and don't let them down. Make sure you offer added value and don't assume you know what the school community needs. You are not there to proselytise but to reflect Christ and even demystify the local church." Coppenhall Methodist