Wenn der Schulbus zu früh kommt, rennt meine Schwester schnell über den Schulhof.

When the school bus comes too early, my sister runs quickly across the schoolyard.

Breakdown of Wenn der Schulbus zu früh kommt, rennt meine Schwester schnell über den Schulhof.

• kommen: to come
• früh: early
• schnell: quickly
• mein: my
• die Schwester: the sister
• wenn: when
• zu: too
• rennen: to run
• über: across
• der Schulbus: the school bus
• der Schulhof: the schoolyard

Questions & Answers about Wenn der Schulbus zu früh kommt, rennt meine Schwester schnell über den Schulhof.

Why is the verb kommt at the end of the clause „Wenn der Schulbus zu früh kommt“?

Because wenn introduces a subordinate clause in German.
In most subordinate clauses, the conjugated verb goes to the end of the clause.

• Main clause word order: Der Schulbus kommt zu früh. (verb in 2nd position)
• Subordinate clause with wenn: Wenn der Schulbus zu früh kommt (verb at the end)

So the pattern is:
wenn + subject + other elements + verb

Why is there a comma, and why does the main clause start with rennt?

A comma must separate the subordinate clause from the main clause:

• Subordinate clause: Wenn der Schulbus zu früh kommt,
• Main clause: rennt meine Schwester schnell über den Schulhof.

When a subordinate clause comes first, the main clause that follows still obeys the verb‑second rule. The first element of the main clause is the entire subordinate clause, so in the main clause the conjugated verb comes next:

• Wenn der Schulbus zu früh kommt, rennt meine Schwester schnell über den Schulhof.

You could also reverse the order:

• Meine Schwester rennt schnell über den Schulhof, wenn der Schulbus zu früh kommt.
  (Now the main clause is first: verb still in 2nd position: Schwester rennt.)

Why is wenn used here and not als, wann, or falls?

These four words are easy to mix up:

• wenn = whenever / if (whenever this happens), used for:

  • repeated events in the present, past, or future
  • conditions
    Here, catching the bus is a repeated / general situation, so wenn fits.

• als = when for a single event in the past:

  • Als der Schulbus zu früh kam, rannte meine Schwester über den Schulhof.
    (On that one occasion in the past when the bus came early…)

• wann = when? (question word, or in indirect questions):

  • Wann kommt der Schulbus? – When does the school bus come?

• falls = in case / if (possibly), more hypothetical:

  • Falls der Schulbus zu früh kommt, rufe mich an.
    (In case the bus comes too early, call me.)

In your sentence we talk about a repeated possible situation (whenever the bus is too early), so wenn is correct.

The verbs are in the present tense (kommt, rennt). Does this talk about the future or a general habit?

German Präsens (present tense) is more flexible than English:

• It can describe a general habit / regular situation:

  • Wenn der Schulbus zu früh kommt, rennt meine Schwester…
    = Whenever the bus comes too early, my sister runs…

• It can also describe near future, depending on context.

Here the meaning is clearly habitual (a repeated pattern). You do not need a future form like wird kommen; the simple present is normal in German for this kind of statement.

What exactly does zu früh mean, and how is zu different from sehr?

• zu früh = too early (earlier than is good or expected, a problem)
• sehr früh = very early (just emphasizes how early it is, but not automatically a problem)

Grammar point:
zu + adjective usually means “too [adjective]”:

• zu klein – too small
• zu laut – too loud
• zu früh – too early

So zu here is not the English "to", but a degree word meaning “too”.

Why is it der Schulbus but den Schulhof? Why the different forms of der?

Both Schulbus and Schulhof are masculine nouns:

• der Schulbus – the school bus (masculine)
• der Schulhof – the schoolyard (masculine)

But the case changes the article:

• der Schulbus is the subject → nominative:

  • Der Schulbus kommt zu früh.
    (Who/what comes too early? → the bus)

• den Schulhof is the object of a preposition of movement → accusative:

  • über den Schulhof (across/over the schoolyard)

Masculine definite article forms:

• Nominative: der (der Schulbus)
• Accusative: den (den Schulhof)

Why is it über den Schulhof and not something like auf dem Schulhof?

Two things are going on: the preposition choice and the case.

1. über with movement:

   • über = over / across
   • With verbs of movement (like rennen), über usually takes the accusative:
     • über den Schulhof rennen – to run across the schoolyard

   This emphasizes motion from one side to the other.

2. Alternative: auf dem Schulhof (dative)

   • auf can mean on / in a place.
   • With location (no movement), you use dative:
     • Sie steht auf dem Schulhof. – She is standing in/on the schoolyard.

So:

• über den Schulhof rennen – running across the yard (movement → accusative)
• auf dem Schulhof sein – being in/on the yard (location → dative)

Why is schnell placed where it is, and could it go somewhere else?

In the main clause you have:

• rennt meine Schwester schnell über den Schulhof.

Typical rule for adverbials: Time – Manner – Place.
Here:

• Manner: schnell (quickly)
• Place: über den Schulhof

German often puts them together as Manner + Place:

• Meine Schwester rennt schnell über den Schulhof.

Other possible placements (all correct, but with slightly different emphasis):

• Meine Schwester rennt über den Schulhof schnell. (less common, sounds a bit marked)
• Meine Schwester rennt schnell. (just says that she runs fast, no place)
• Schnell rennt meine Schwester über den Schulhof. (puts strong emphasis on quickly)

What you cannot do is move schnell to the very front and keep rennt from being in the second position of the main clause after the comma. The finite verb must remain in second position in the main clause.

Could we use läuft instead of rennt? What’s the difference?

Both are often translated as to run or to walk, but they’re not identical:

• rennen = to run fast, to sprint, to dash.
  It clearly implies speed / hurry.

• laufen is broader:

  • can mean to walk (especially in everyday speech: Ich laufe zur Schule = I walk to school)
  • can also mean to run (as in Ich laufe 5 Kilometer = I run 5 km)

In this sentence, the idea is that she is in a hurry because the bus is too early, so rennt (runs / dashes) is more precise and vivid than läuft.
You could say läuft, but it would sound less urgent.

Why is meine Schwester written like that and not meiner Schwester?

meine Schwester is the subject of the main clause:

• Wer rennt? (Who runs?) → meine Schwester
  Subjects are in the nominative case.

The possessive mein- declines like the indefinite article ein:

• Feminine, nominative: meine Schwester
• Feminine, dative: meiner Schwester (e.g. Ich helfe meiner Schwester.)

So in your sentence, nominative is required → meine Schwester is correct.

Why are Schulbus and Schulhof capitalized, but schnell and zu früh are not?

German capitalizes all nouns, regardless of their position in the sentence:

• der Schulbus, der Schulhof, die Schwester → all capitalized
• schnell, früh, zu are not nouns, so they remain lowercase:
  • schnell – adverb / adjective
  • früh – adjective / adverb
  • zu – particle (here, meaning “too”)

Only:

• The first word of the sentence is capitalized (Wenn…)
• All nouns and noun-like words are capitalized.