Google Sheets Query across sheets using checkboxes to limit results - if-statement

Question

I am making a mini-search engine in Google Sheets. I have information in 3 sheets (6th Grade, 7th Grade, 8th Grade).
In the past, I had a Combined sheet that combined the information from each sheet. However, as I add additional sheets for grades 1-5, the amount of information returned will be excessive. I want to allow the user to use checkboxes to identify which grades they want results from.
Here is the workbook.
I've added sheets for all the grades by copying the data from 6th, 7th, and 8th. The format of the data will be the same once I get my hands on it.
Here is the formula I've been playing around with:
=iferror(If(D2=True,Query(
Kindergarten!A:I,"Select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0",
),
Query(
{Kindergarten!A:I;'1st'!A:I;'2nd'!A:I},"Select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0",
),
"No Matches, try a different search"))

Answer 1

you did not mention what you want to search in Search cell, but the formula would be:
=IFERROR(QUERY({
IF(D2=TRUE, IFERROR(QUERY({Kindergarten!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(E2=TRUE, IFERROR(QUERY({'1st'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(F2=TRUE, IFERROR(QUERY({'2nd'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(G2=TRUE, IFERROR(QUERY({'3rd'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(H2=TRUE, IFERROR(QUERY({'4th'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(C4=TRUE, IFERROR(QUERY({'5th'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(D4=TRUE, IFERROR(QUERY({'6th'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(E4=TRUE, IFERROR(QUERY({'7th'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(F4=TRUE, IFERROR(QUERY({'8th'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(G4=TRUE, IFERROR(QUERY({'9th and 10th'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""});
IF(H4=TRUE, IFERROR(QUERY({'11th and 12th'!A:I}, "select Col1,Col2,Col3,Col4,Col5,Col6,Col7,Col8 where Col9>0", 0), {"","","","","","","",""}), {"","","","","","","",""})},
"where Col1 is not null", 0), "No Matches, try a different search")