This is a decision the church/school will need to make after they study the matter. I can pass along the following information from answers to similar questions that contained some concern and caution.
Congregational fundraising in the community can reinforce what many wrongly think in the first place—that “all the church is concerned about is money.” Congregational fundraising in the community can reinforce work-righteous thinking in some of the unchurched, leading them to think that “I’ve given to God, so I’ve done my duty.” Congregational fundraising in the community can undermine a church’s efforts to encourage its members to grow in their management of God’s blessings if they grow instead in their reliance on community revenue.
There certainly is a danger that fundraisers can fuel the idea that giving involves the possibility of getting or receiving something in return. It is important to keep in mind the motive for giving. It is love for God and gratitude for his love that provides the motivation for giving back to God what is his in the first place (2 Corinthians 5:15; 1 John 4:19).
If the church/school is looking for financial support from its own constituency and not the community in any way, free will offerings can go a long way in funding a youth field trip. Congregational members can be presented with the special opportunity to give towards this cause, and God’s people will respond as they are moved. An approach like this eliminates difficulties associated with raffles and fundraising in general.