Spot the grammatical mistake in a sentence and pick the correct replacement for the highlighted error. 45 problems across three tiers: Middle School (subject-verb agreement, apostrophes, comma splices, there/their/they're, double negatives), High School (dangling modifiers, parallel structure, who/whom, subjunctive mood, lie/lay), and SAT Prep (idioms, concision, that/which, restrictive clauses, advanced agreement patterns).
Read the Sentence
Each sentence has one underlined portion marked in red. This is the error candidate โ sometimes it IS wrong, and sometimes it's testing whether you recognize correct usage. Your job is to replace it with the best option.
Choose a Difficulty
Middle School targets the core errors students learn in grades 6โ8: apostrophes, comma splices, homophones, and basic agreement. High School introduces the trickier patterns from grades 9โ12: modifiers, parallelism, subjunctive, and the who/whom rule. SAT Prep covers the high-frequency errors on the SAT Writing section, including idiom precision, wordiness, and restrictive vs. nonrestrictive clauses.
Identify the Error Type
The colored category badge tells you what kind of error to look for. AGREEMENT: check if subjects and verbs or pronouns and antecedents match in number. USAGE: check if the right word is used (especially homophones). STRUCTURE: check sentence construction โ is it a run-on, a broken parallel, or a dangling modifier? STYLE: check if the phrasing is precise and concise.
Check and Learn
After answering, the grammar rule appears and โ for incorrect answers โ the fully corrected sentence is shown. This is the most valuable part: seeing the corrected sentence in context helps you internalize the pattern, not just the rule.
45 Problems Across 3 Tiers
Middle School covers the most frequent everyday errors: subject-verb agreement with collective nouns and intervening phrases, apostrophe misuse (its vs. it's, hers vs. her's), there/their/they're, comma splices, double negatives, and incorrect pronoun case after prepositions. High School adds dangling and misplaced modifiers, parallel structure in lists, the who/whom distinction, subjunctive mood (if I were), lie vs. lay, nonrestrictive clause punctuation, and the farther/further distinction. SAT Prep targets sophisticated writing errors tested on standardized exams: wordiness (due to the fact that โ because), that/which distinction, advanced agreement (board along with its advisers), not only...but also subject proximity, suggest + gerund, and principal/principle confusion.
Highlighted Error Display
Each question shows a full sentence with the error portion underlined in red. You don't have to find the error yourself โ you have to choose the correct replacement from four options. This mirrors the format of SAT Writing questions and standard grammar editing exercises, making it both realistic and immediately clear what to fix.
4 Error Types โ Color-Coded
AGREEMENT (rose) covers subject-verb, pronoun-antecedent, and pronoun-case errors. USAGE (amber) covers word choice: there/their/they're, its/it's, affect/effect, further/farther, principal/principle, idioms, and verb tense. STRUCTURE (blue) covers sentence-level issues: comma splices, dangling modifiers, parallel structure, nonrestrictive clause punctuation, and word order. STYLE (purple) covers SAT-level concision and register: replacing wordy phrases, choosing the most precise word, and subordination.
Editorial Proofreader Theme
The game uses a warm cream paper background with red proofreading marks as accents โ evoking the classic experience of a teacher's red pen. The lobby shows a before/after example sentence demonstrating exactly how the game works: error highlighted in red, correct form revealed in green below.
Middle School: subject-verb agreement with collective nouns and intervening phrases, its/it's, there/their/they're, possessive pronouns (hers not her's), comma splices, double negatives, pronoun case after prepositions, who/whom basics, and inverted sentence agreement. High School: dangling modifiers, parallel structure in lists, the company/its agreement, who/whom with object test, subjunctive mood (if I were), semicolon with conjunctive adverbs (however), lay/laid vs. lie, nonrestrictive clause commas, farther/further, pronoun ambiguity, different from vs. different than, neither...nor agreement, and misplaced 'only'. SAT: subject agreement with intervening phrases, concision, that/which, dangling modifiers, idiom precision (in accordance with), should have vs. should of, comparative vs. superlative, suggest + gerund, not only...but also agreement, comma splices, that/which with commas, affect/effected, board + along with agreement, and principal/principle.
Use 'that' for restrictive clauses (essential information, no commas): 'The book that won the prize is sold out.' Use 'which' for nonrestrictive clauses (extra info, with commas): 'The book, which won the prize, is sold out.' A good test: if you can remove the clause without changing which thing is being discussed, use 'which' + commas. If removing it changes the meaning, use 'that' without commas.
Substitute 'he/she' or 'him/her' in the clause. If 'he/she' fits, use 'who'. If 'him/her' fits, use 'whom'. Example: 'Who/Whom did she call?' โ 'She called him.' โ Use 'whom'. Example: 'Who/Whom is calling?' โ 'He is calling.' โ Use 'who'. Another memory trick: 'whom' ends in 'm', like 'him' โ both are objective case.
It's the subjunctive mood, used for hypothetical or contrary-to-fact conditions. 'If I were you' is correct because you're NOT actually the other person โ it's a hypothetical. 'If I was' would imply you possibly were that person, which is factually impossible. The subjunctive also appears in 'I wish it were Friday', 'She insisted that he be present', and formal conditionals. It's one of the few remaining subjunctive forms in English.
Correct answers earn 10 pts (Middle School), 15 pts (High School), or 20 pts (SAT Prep). Consecutive correct answers add a 5-point streak bonus per answer after the first. A wrong answer resets the streak to zero.
Yes โ the SAT Writing section tests many of these exact patterns. The SAT Prep tier focuses specifically on the error types most frequently tested: concision (wordiness), that/which, subject-verb agreement with complex noun phrases, idiomatic preposition use, and correlative conjunction agreement. The format (sentence with underlined portion, four replacement choices) directly mirrors the SAT Writing question style.