Hij is erin geslaagd om zijn scriptie op tijd in te leveren.

Because this expression uses zijn in the perfect tense: geslaagd zijn.

So:

• Hij slaagt = he succeeds
• Hij is geslaagd = he succeeded / he has succeeded

This is something you mostly have to learn with the verb or expression. In Dutch, some verbs form the perfect tense with zijn instead of hebben, and slagen in this meaning is one of them.

A very common parallel is:

• Hij is geslaagd voor het examen = he passed the exam

It is the same verb, but used in a different pattern.

Common uses:

• slagen voor een examen = to pass an exam
• ergens in slagen = to succeed in something
• erin slagen om iets te doen = to succeed in doing something

So the core idea is still to be successful.
In this sentence, geslaagd does not mean graduated or passed by itself. It means managed to / succeeded in because of the construction erin slagen om ... te ...

Erin is a pronominal adverb: er + in.

It refers to the thing he succeeded in. In English, we often just say succeeded in doing it or managed to do it, but Dutch uses erin very naturally here.

The underlying structure is:

• slagen in iets = succeed in something

When that iets is not a noun but an action expressed later in the sentence, Dutch often uses erin:

• Hij is erin geslaagd om zijn scriptie op tijd in te leveren.

So erin points forward to the action zijn scriptie op tijd in te leveren.

No, not in normal Dutch.

You would not say:

• Hij is in geslaagd ... ❌

You need the combined form erin here.

That is because Dutch usually combines a preposition like in with er, daar, hier, or waar:

• erin = in it
• daarin = in that
• waarin = in what / in which

So with slagen in iets, when iets is not named as a noun, erin is the normal choice.

Often, om is optional here.

Both of these are common:

• Hij is erin geslaagd om zijn scriptie op tijd in te leveren.
• Hij is erin geslaagd zijn scriptie op tijd in te leveren.

So:

• om is very common and sounds natural
• leaving out om is also normal
• te must stay

You can think of om ... te as introducing the infinitive clause, similar to English to ..., though the Dutch structure is not identical.

Because inleveren is a separable verb.

Its parts are:

• in
  • leveren = inleveren = to hand in / submit

With separable verbs, te goes between the prefix and the main verb:

• in te leveren ✅
• te inleveren ❌

Compare:

• Hij levert zijn scriptie in. = He hands in his thesis.
• Hij wil zijn scriptie inleveren. = He wants to hand in his thesis.
• Hij probeert zijn scriptie in te leveren. = He tries to hand in his thesis.

So this sentence follows the normal pattern for separable verbs with te.

Scriptie usually means a thesis, dissertation, or final paper, depending on the educational context.

For many learners, it looks like English script, but it does not normally mean that.

In university contexts, scriptie is the substantial piece of academic writing a student submits, often at the end of a program.

So in this sentence, zijn scriptie means his thesis/final paper.

Because Dutch usually puts the verbal part at the end of the clause, and the object and adverb come before it.

Inside the infinitive clause, the order is:

• zijn scriptie = object
• op tijd = adverbial phrase
• in te leveren = infinitive verb phrase

So the clause is built like this:

• om [zijn scriptie] [op tijd] [in te leveren]

That is a very normal Dutch pattern.

A helpful rule of thumb:

• non-verbal information comes first
• the infinitive verb cluster comes at the end

It can match either English phrase depending on context.

In this sentence, with handing in a thesis, op tijd most naturally means:

• on time
• before the deadline
• not late

So the practical meaning is: he managed to submit it by the required time.

Dutch op tijd is often broader than English on time, so context decides the best translation.

No. In this sentence, the second zijn means his.

So:

• Hij is = He is / He has
• zijn scriptie = his thesis

Dutch zijn can be:

• a form of the verb zijn = to be
• a possessive pronoun = his

Here you see both in the same sentence, but they are doing different jobs.

A useful way to break it down is:

• Hij is geslaagd = He succeeded / He has succeeded
• erin = in it / in that
• om ... in te leveren = to hand in ...
• zijn scriptie = his thesis
• op tijd = on time / before the deadline

So the grammar pattern is:

• iemand is erin geslaagd (om) iets te doen

Example pattern:

• Zij is erin geslaagd de trein te halen.
• Wij zijn erin geslaagd het probleem op te lossen.

This is a very common Dutch way to say manage to do something or succeed in doing something.