You already split a sentence into two halves. Inside each half, one single word is doing the real work. This is how you find it.
Not started yet.
The complete subject is every word telling you who or what the sentence is about, and inside it one main word carries the meaning. That word is the simple subject. The complete predicate is everything said about that subject, and inside it the verb is the simple predicate.
Almost every grammar skill after this one is stated in terms of these two words. Subject and verb agreement, compound subjects, compound predicates and finding the subject in a question all assume a student can already point at the one word each half is built on.
Picking a noun out of the describing phrase instead of the one the sentence is about. In the mechanic under the left wing, a student marks wing, because it is a noun and it is close to the verb. Ask him what tightened the bolt, and he corrects himself.
The simple subject is the main word in the complete subject. The simple predicate is the verb.
You already know a sentence splits into two halves. The simple subject is the one main word inside the green half, and it is almost always a noun or a pronoun. The simple predicate is the verb inside the orange half, the word that says what the subject does or what it is. Everything else in either half is there to describe, and describing words are not the answer. When a verb travels with a helper, as in has tightened or is flying, the helper and the verb go together and count as one simple predicate.
Run this test. Say the sentence with only two words. Keep the one word the sentence is about and the one word saying what it does, and drop everything else. If what is left still makes sense as a tiny sentence, you have found both.
Press play to have it read to you. The line being read lights up, so you can follow along.
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The same sentences you just heard. Green is the simple subject and orange is the simple predicate.
Saturday morning at the little airfield is the busiest part of the week.
The sentence is about a morning, not an airfield. And is counts as the verb even though nothing happens.
Two students near the fence watch a yellow trainer taxi past them.
Near the fence tells you which students, so fence is not the answer. Watch is what they do.
Her student flies the whole circuit without a single word.
A short green half this time. One word in, one word out.
The last plane rolls into the hangar at six o'clock.
Last describes the plane, and describing words are never the simple subject.
Four done for you. The line under each one says how you could have known.
The mechanic under the left wing tightens a bolt for the third time.
Who or what is this about? A mechanic. Under the left wing only says which one, so wing is a trap sitting right beside the verb. What does he do? He tightens.
The instructor in the back seat writes something on her clipboard.
Seat and clipboard are both nouns and neither is what the sentence is about. Strip it to two words and you get instructor writes, which still makes sense.
The old windsock above the fuel pump twists toward the north.
Old describes the windsock and above the fuel pump says where it is. Neither survives the two-word test. Windsock twists does.
Every pilot on the field checks that windsock before takeoff.
Every is a describing word, so it is not the simple subject even though it comes first. The pilot is who this is about, and checking is what he does.
Two parts, like a worksheet. Part A lays the words out for you. Part B does not. A wrong answer tells you why and lets you go again, so nothing here counts against you.
Six sentences. The words are laid out for you. Tap the one the question asks for.
Six more sentences, and this time nothing is laid out. Tap the word in the line.