Database schema:

CREATE TABLE donations (
	donationid TEXT NOT NULL -- example: ['000000a91a14ed37bef82e125c102e77', '000013be53ed7382ed5d5975eb86eb85'],
	projectid TEXT -- example: ['ffffac55ee02a49d1abc87ba6fc61135', 'ffff97ed93720407d70a2787475932b0'],
	donor_acctid TEXT -- example: ['22cbc920c9b5fa08dfb331422f5926b5', '521f1830a77c9dbbf8119d99c6206a16'],
	donor_city TEXT -- example: ['Peachtree City', 'Rockville'],
	donor_state TEXT -- example: ['GA', 'MD'],
	donor_zip TEXT -- example: ['30269', '20853'],
	is_teacher_acct TEXT -- example: ['f', 't'],
	donation_timestamp DATETIME -- example: ['2011-11-04 07:54:21.552000', '2011-08-25 14:27:34.807000'],
	donation_to_project REAL -- example: ['26.83', '42.5'],
	donation_optional_support REAL -- example: ['7.5', '4.73'],
	donation_total REAL -- example: ['31.56', '50.0'],
	dollar_amount TEXT -- example: ['under_10', '10_to_100'],
	donation_included_optional_support TEXT -- example: ['f', 't'],
	payment_method TEXT -- example: ['no_cash_received', 'creditcard'],
	payment_included_acct_credit TEXT -- example: ['f', 't'],
	payment_included_campaign_gift_card TEXT -- example: ['f', 't'],
	payment_included_web_purchased_gift_card TEXT -- example: ['f', 't'],
	payment_was_promo_matched TEXT -- example: ['f', 't'],
	via_giving_page TEXT -- example: ['f', 't'],
	for_honoree TEXT -- example: ['f', 't'],
	donation_message TEXT -- example: ['I gave to this project because I support the effor', 'I donated because I want to support kids in Georgi'],
	PRIMARY KEY (donationid), 
	CONSTRAINT fk_donations_projects FOREIGN KEY(projectid) REFERENCES projects (projectid)
)


CREATE TABLE essays (
	projectid TEXT -- example: ['ffffac55ee02a49d1abc87ba6fc61135', 'ffffc4f85b60efc5b52347df489d0238'],
	teacher_acctid TEXT -- example: ['947066d0af47e0566f334566553dd6a6', 'c24011b20fc161ed02248e85beb59a90'],
	title TEXT -- example: ["Recording Rockin' Readers", 'iMath'],
	short_description TEXT -- example: ['It is imperative that teachers bring technology in', 'Can you imagine having to translate everything you'],
	need_statement TEXT -- example: ['My students need four iPods.', 'My students need a camcorder. '],
	essay TEXT -- example: ['I am a fourth year fifth grade math teacher. The s', 'Can you imagine having to translate everything you']
)


CREATE TABLE projects (
	projectid TEXT NOT NULL -- example: ['00002bff514104264a6b798356fdd893', '00001ccc0e81598c4bd86bacb94d7acb'],
	teacher_acctid TEXT -- example: ['864eb466462bf704bf7a16a585ef296a', '42d43fa6f37314365d08692e08680973'],
	schoolid TEXT -- example: ['c0e6ce89b244764085691a1b8e28cb81', 'd711e47810900c96f26a5d0be30c446d'],
	school_ncesid TEXT -- example: ['063627006187', '483702008193'],
	school_latitude REAL -- example: ['36.57634', '32.911179'],
	school_longitude REAL -- example: ['-119.608713', '-96.72364'],
	school_city TEXT -- example: ['Dallas', 'Selma'],
	school_state TEXT -- example: ['TX', 'CA'],
	school_zip INTEGER -- example: ['93662', '75243'],
	school_metro TEXT -- example: ['rural', 'urban'],
	school_district TEXT -- example: ['Selma Unified Sch District', 'Richardson Ind School District'],
	school_county TEXT -- example: ['Dallas', 'Fresno'],
	school_charter TEXT -- example: ['f', 't'],
	school_magnet TEXT -- example: ['f', 't'],
	school_year_round TEXT -- example: ['f', 't'],
	school_nlns TEXT -- example: ['f', 't'],
	school_kipp TEXT -- example: ['f', 't'],
	school_charter_ready_promise TEXT -- example: ['f', 't'],
	teacher_prefix TEXT -- example: ['Mrs.', 'Mr.'],
	teacher_teach_for_america TEXT -- example: ['f', 't'],
	teacher_ny_teaching_fellow TEXT -- example: ['f', 't'],
	primary_focus_subject TEXT -- example: ['Literacy', 'Literature & Writing'],
	primary_focus_area TEXT -- example: ['Literacy & Language', 'History & Civics'],
	secondary_focus_subject TEXT -- example: ['College & Career Prep', 'ESL'],
	secondary_focus_area TEXT -- example: ['Literacy & Language', 'Applied Learning'],
	resource_type TEXT -- example: ['Technology', 'Books'],
	poverty_level TEXT -- example: ['highest poverty', 'high poverty'],
	grade_level TEXT -- example: ['Grades PreK-2', 'Grades 6-8'],
	fulfillment_labor_materials REAL -- example: ['35.0', '30.0'],
	total_price_excluding_optional_support REAL -- example: ['296.47', '555.81'],
	total_price_including_optional_support REAL -- example: ['653.89', '348.79'],
	students_reached INTEGER -- example: ['22', '32'],
	eligible_double_your_impact_match TEXT -- example: ['f', 't'],
	eligible_almost_home_match TEXT -- example: ['f', 't'],
	date_posted DATE -- example: ['2014-05-12', '2014-05-11'],
	PRIMARY KEY (projectid)
)


CREATE TABLE resources (
	resourceid TEXT NOT NULL -- example: ['0000037fecc4461faf0e49328ae66661', '0000046b69c683354ca46b30db5c558e'],
	projectid TEXT -- example: ['ffffac55ee02a49d1abc87ba6fc61135', 'ffffc4f85b60efc5b52347df489d0238'],
	vendorid INTEGER -- example: ['430', '82'],
	vendor_name TEXT -- example: ['Woodwind and Brasswind', 'Best Buy for Business'],
	project_resource_type TEXT -- example: ['Supplies', 'Technology'],
	item_name TEXT -- example: ['iPod nano 4th Gen 8GB (Black)', 'Sony bloggie MHS-FS1 - camcorder - internal flash '],
	item_number TEXT -- example: ['249995.001', 'BB11216668'],
	item_unit_price REAL -- example: ['148.0', '149.0'],
	item_quantity INTEGER -- example: ['1', '4'],
	PRIMARY KEY (resourceid), 
	CONSTRAINT fk_resources_projects FOREIGN KEY(projectid) REFERENCES projects (projectid)
)

Question: Among the projects whose donators are teachers, what is the percentage of projects that affected more than 30 students?
Evidence: donors are teachers refers to is_teacher_acct = 't'; affect more than 30 students refers to students_reached>30; Percentage = Divide(Count(students_reached>30), Count(students_reached))*100

SQL:
SELECT CAST(SUM(CASE WHEN T1.students_reached > 30 THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.projectid) FROM projects AS T1 INNER JOIN donations AS T2 ON T1.projectid = T2.projectid WHERE T2.is_teacher_acct = 't'